AstraZeneca, the British pharmaceuticals giant, will pay $323m (£214m) to buy a specialist US drugs company, in a deal that it hopes will help support its revenues as many patents expire.

The FTSE 100 group will pay $12.70 per share for Omthera Pharmaceuticals, which is based in Princeton, New Jersey, and floated on the Nasdaq index in April at $8 a share. The purchase price marks a premium of 88pc to Omthera’s closing price on Friday, AstraZeneca said.

The deal brings AstraZeneca a product called Epanova, a fish oil-based treatment which could be used to treat patients with high levels of triglycerides, fats in the blood which are bad for the heart. If Epanova hits global sales targets, extra pay-outs to shareholders could take the total deal cost to $443m.

Pascal Soriot, chief executive of AstraZeneca said: “The number of people with elevated triglyceride levels is rising rapidly across the world, due in part to the increasing prevalence of obesity and diabetes. There is a clear need for effective and convenient alternatives to some of the existing treatments.”

The deal comes as AstraZeneca, like its rivals, is faced with the headache of patents expiring on many of the drugs it produces. The long-term prospects for the healthcare industry are sound, supported by aging populations around the world and the rise of the middle class in Asia. However, companies are struggling to drive growth today.

Pre-tax profits at AstraZeneca fell 36pc to $1.3bn in the first quarter of 2013, as it lost the exclusivity on several large drug products. The biggest damage was caused by loss of exclusivity on antipyschotic medicine Seroquel and heart drug Atacand in many markets, and on cholesterol fighter Crestor, a statin, in Canada.

Shore Capital analysts said the acquisition, via Omthera, of Epanova should help the group in the latter market. “The addition of an omega-3 fatty acid preparation will serve to flesh out the high cholesterol franchise currently dominated by the statin Crestor,” they said.

The deal also represents one of the first high-profile moves by Mr Soriot, who joined the company last October, following the resignation of the former chief executive David Brennan – the first victim of the so-called Shareholder Spring.

In March, Mr Soriot outlined a new strategy for the group, announcing that AstraZeneca planned to double the number of drugs in late-stage development by 2016. As part of the overhaul, AstraZeneca said that it was restructuring its sales and administration division, taking the total job losses it announced that week alone to 3,900.

The strategy - read as trusting scientists to come up with the next wonder-drug - has been seen as higher risk than trying to drive growth through acquisitions. Deutsche Bank analysts call “execution” a key share price risk.

While deals are not off the table, as yesterday’s announcement showed, they are not expected to be the company’s focus. The market reacted positively to the news of the purchase, which Barclays analysts called “strategically sensible”.

The shares were also supported by news of a temporary blockage on US sales of rival generic versions of the group’s asthma drug Pulmicort Repsules, which was announced late on Friday.